U.S. patent application number 10/931642 was filed with the patent office on 2006-03-02 for magnetic recording disk with antiferromagnetically coupled master layer including copper.
Invention is credited to Xiaoping Bian, Mary Frances Doerner, Tetsuya Kanbe, Mark Mercado, Mohammad Mirzamaani, Adam Polcyn, Kai Tang.
Application Number | 20060046102 10/931642 |
Document ID | / |
Family ID | 35943627 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060046102 |
Kind Code |
A1 |
Bian; Xiaoping ; et
al. |
March 2, 2006 |
Magnetic recording disk with antiferromagnetically coupled master
layer including copper
Abstract
An antiferromagnetically coupled (AFC) magnetic recording medium
with an AFC master layer comprising at least two magnetic layers
with the top magnetic layer including copper is described. The
slave layer is separated from the master layer structure by a
nonmagnetic spacer layer selected to antiferromagnetically couple
the layers. The master layer structure according to the invention
includes a bottom and top layer of distinct ferromagnetic
materials. Preferably, the top layer of the master layer is a
cobalt alloy including from 1 to 5 at. % copper with an example
being CoPt.sub.13Cr.sub.20B.sub.8Cu.sub.2. The AFC magnetic layer
structure can be used with a variety of substrates including
circumferentially textured glass and NiP/AlMg.
Inventors: |
Bian; Xiaoping; (San Jose,
CA) ; Doerner; Mary Frances; (Santa Cruz, CA)
; Kanbe; Tetsuya; (Cupertino, CA) ; Mercado;
Mark; (Morgan Hill, CA) ; Mirzamaani; Mohammad;
(San Jose, CA) ; Polcyn; Adam; (San Jose, CA)
; Tang; Kai; (San Jose, CA) |
Correspondence
Address: |
MARLIN KNIGHT
P. O. BOX 1320
PIONEER
CA
95666
US
|
Family ID: |
35943627 |
Appl. No.: |
10/931642 |
Filed: |
August 31, 2004 |
Current U.S.
Class: |
428/828.1 ;
428/831.1; 428/836.3; G9B/5.241; G9B/5.288 |
Current CPC
Class: |
G11B 5/73921 20190501;
G11B 5/66 20130101; G11B 5/7379 20190501; G11B 5/73913 20190501;
G11B 5/737 20190501; G11B 5/656 20130101; G11B 5/7369 20190501 |
Class at
Publication: |
428/828.1 ;
428/831.1; 428/836.3 |
International
Class: |
G11B 5/66 20060101
G11B005/66 |
Claims
1. A thin film magnetic recording medium comprising: at least one
underlayer; a slave ferromagnetic layer deposited on the
underlayer; a nonmagnetic spacer layer adjacent to the slave
ferromagnetic layer; and a master layer structure including: a
bottom layer of ferromagnetic material adjacent to the spacer
layer; and a top layer of ferromagnetic adjacent to the bottom
layer, the bottom and top layers of ferromagnetic material being
antiferromagnetically coupled to the slave ferromagnetic layer, the
top layer being an alloy including cobalt, platinum, chromium and
copper.
2. The thin film magnetic recording medium of claim 1 wherein the
top layer has from 1 to 5 at. % copper (Cu).
3. The thin film magnetic recording medium of claim 1 wherein the
top layer of ferromagnetic material includes boron.
4. The thin film magnetic recording medium of claim 1 wherein the
bottom layer of ferromagnetic material comprises CoPtCrB.
5. The thin film magnetic recording medium of claim 1 further
comprising a circumferentially textured glass substrate and wherein
the top layer of ferromagnetic material has a lower magnetic moment
than the bottom layer of ferromagnetic material.
6. The thin film magnetic recording medium of claim 5 further
comprising a seed layer of RuAl deposited prior to the underlayer
and wherein the underlayer is adjacent to the seed layer.
7. The thin film magnetic recording medium of claim 5 further
comprising an amorphous or nanocrystalline pre-seed layer of CrTi,
CrTa or AlTi deposited prior to the seed layer and wherein the seed
layer is adjacent to the pre-seed layer.
8. The thin film magnetic recording medium of claim 1 wherein the
slave ferromagnetic layer is CoCr.
9. The thin film magnetic recording medium of claim 1 further
comprising a circumferentially textured NiP/AlMg substrate and
wherein the top layer of ferromagnetic material has a higher
magnetic moment than the bottom layer of ferromagnetic
material.
10. The thin film magnetic recording medium of claim 9 wherein the
slave ferromagnetic layer comprises CoCrZr.
11. The thin film magnetic recording medium of claim 9 including
one or more underlayers of Cr, CrMo or CrMoB.
12. A disk drive comprising: a magnetic transducer including a read
and a write head for reading and writing data on a thin film disk;
and a thin film magnetic recording medium on the thin film disk
comprising: at least one underlayer; a slave ferromagnetic layer
deposited on the underlayer; a nonmagnetic spacer layer adjacent to
the slave ferromagnetic layer; and a master layer structure
including: a bottom layer of ferromagnetic material adjacent to the
spacer layer; and a top layer of ferromagnetic adjacent to the
bottom layer, the bottom and top layers of ferromagnetic material
being antiferromagnetically coupled to the slave ferromagnetic
layer, the top layer being an alloy including cobalt, platinum,
chromium and copper.
13. The disk drive of claim 12 wherein the top layer has from 1 to
5 at. % copper (Cu).
14. The disk drive of claim 12 wherein the top layer of
ferromagnetic material includes boron.
15. The disk drive of claim 12 wherein the bottom layer of
ferromagnetic material comprises CoPtCrB.
16. The disk drive of claim 1 wherein the thin film disk further
comprises a circumferentially textured glass substrate and wherein
the top layer of ferromagnetic material has a lower magnetic moment
than the bottom layer of ferromagnetic material.
17. The disk drive of claim 16 wherein the thin film magnetic
recording medium further comprises a seed layer of RuAl deposited
prior to the underlayer and wherein the underlayer is adjacent to
the seed layer.
18. The disk drive of claim 16 wherein the thin film magnetic
recording medium further comprises an amorphous or nanocrystalline
pre-seed layer of CrTi, CrTa or AlTi deposited prior to the seed
layer and wherein the seed layer is adjacent to the pre-seed
layer.
19. The disk drive of claim 16 wherein the slave ferromagnetic
layer is CoCr.
20. The disk drive claim 12 wherein the thin film magnetic
recording medium further comprises a circumferentially textured
NiP/AlMg substrate and wherein the top layer of ferromagnetic
material has a higher magnetic moment than the bottom layer of
ferromagnetic material.
21. The disk drive of claim 20 wherein the slave ferromagnetic
layer comprises CoCrZr.
22. The disk drive of claim 20 wherein the thin film magnetic
recording medium includes one or more underlayers of Cr, CrMo or
CrMoB.
23. A method of fabricating a thin film magnetic recording medium
comprising: depositing at least one thin film underlayer;
depositing a slave ferromagnetic layer on the underlayer;
depositing a nonmagnetic spacer layer on the slave ferromagnetic
layer; depositing a bottom layer of ferromagnetic material on the
spacer layer; and depositing a top layer of ferromagnetic on the
bottom layer, the bottom and top layers of ferromagnetic material
being antiferromagnetically coupled to the slave ferromagnetic
layer, the top layer being an alloy including cobalt, platinum,
chromium and copper.
Description
FIELD OF THE INVENTION
[0001] The invention relates to magnetic thin film media with
antiferromagnetically coupled ferromagnetic layers and more
particularly to materials used for the ferromagnetic thin films in
such media.
BACKGROUND OF THE INVENTION
[0002] A typical prior art a disk drive system 10 using
longitudinal recording is illustrated in FIG. 1. In operation the
magnetic transducer (head) 20 is supported by the suspension (not
shown) as it flies above the rotating disk 16. The magnetic
transducer 20, usually called a "head" or "slider," is composed of
elements that perform the task of writing magnetic transitions (the
write head 23) and reading the magnetic transitions (the read head
12). The magnetic transducer 20 is positioned over points at
varying radial distances from the center of the disk 16 to read and
write circular tracks (not shown). The disk 16 is attached to a
spindle (not shown) driven by a spindle motor (not shown) to rotate
the disk 16. The disk 16 comprises a substrate 26 on which a
plurality of thin films 21 are deposited. The thin films 21 include
ferromagnetic material in which the write head 23 records the
magnetic transitions in which information is encoded.
[0003] The conventional disk 16 includes substrate 26 of glass or
AlMg with an electroless coating of Ni.sub.3P that has been highly
polished. The thin films 21 on the disk 16 typically include a
chromium or chromium alloy underlayer and at least one
ferromagnetic layer based on various alloys of cobalt. For example,
a commonly used alloy is CoPtCr. Additional elements such as
tantalum and boron are often used in the magnetic alloy. A
protective overcoat layer is used to improve wearability and
corrosion resistance. Various seed layers, multiple underlayers
have all been described in the prior art. More recently
antiferromagnetically coupled media have been described. Seed
layers have been suggested for use with nonmetallic substrate
materials such as glass. Typically the seed layer is the first
crystalline film deposited in the structure and is followed by the
underlayer. Materials proposed for use as seed layers include
chromium, titanium, tantalum, MgO, tungsten, CrTi, FeAl, NiAl and
RuAl. The use of pre-seed layers 31 is relatively recent practice.
The pre-seed layer is an amorphous or nanocrystalline thin film
that is deposited on the substrate prior to the crystalline seed
layer. The preseed layer helps to improve media magnetic properties
and recording performance and provide excellent mechanical
properties for the hard disk.
[0004] In U.S. Pat. No. 6,280,813 to Carey, et al. a layer
structure is described that includes at least two ferromagnetic
films antiferromagnetically coupled together across a
nonferromagnetic coupling/spacer film. In general, it is said that
the exchange coupling oscillates from ferromagnetic to
antiferromagnetic with increasing coupling/spacer film thickness
and that the preferred 6 Angstrom thickness of the ruthenium
coupling/spacer layer was selected because it corresponds to the
first antiferromagnetic peak in the oscillation for the particular
thin film structure. Materials that are appropriate for use as the
nonferromagnetic coupling/spacer films include ruthenium (Ru),
chromium (Cr), rhodium (Rh), iridium (Ir), copper (Cu), and their
alloys. Because the magnetic moments of the two
antiferromagnetically coupled films are oriented antiparallel, the
net remanent magnetization-thickness product (M.sub.rt) of the
recording layer is the difference in the M.sub.rt values of the two
ferromagnetic films. This reduction in M.sub.rt is accomplished
without a reduction in the thermal stability of the recording
medium because the volumes of the grains in the
antiferromagnetically coupled films add constructively. An
embodiment of the structure includes two ferromagnetic CoPtCrB
films, separated by a Ru spacer film having a thickness selected to
maximize the antiferromagnetic exchange coupling between the two
CoPtCrB films. The top ferromagnetic layer is designed to have a
greater M.sub.rt than the bottom ferromagnetic layer, so that the
net moment in zero applied magnetic field is low, but nonzero. The
Carey '813 patent also states that the antiferromagnetic coupling
is enhanced by a thin (5 angstroms) ferromagnetic cobalt interface
layer added between the coupling/spacer layer and the top and/or
bottom ferromagnetic layers. The patent mentions, but does not
elaborate on the use CoCr interface layers.
[0005] In U.S. Pat. No. 6,567,236 to Doerner, et al. an
antiferromagnetically coupled layer structure for magnetic
recording wherein the top ferromagnetic structure is a bilayer
structure including a relatively thin first sublayer of
ferromagnetic material in contact with the coupling/spacer layer.
The first sublayer has a higher magnetic moment than the second
sublayer. The second sublayer has a lower magnetic moment and is
much thicker than the first sublayer with a composition and
thickness selected to provide the M.sub.rt when combined with first
sublayer that is needed for the overall magnetic structure. A
preferred embodiment of a layer structure according to the patent
is a pre-seed layer preferably of CrTi; a seed layer preferably of
RuAl; an underlayer preferably of CrTi; a bottom ferromagnetic
layer preferably of CoCr; an antiferromagnetic coupling/spacer
layer preferably of Ru; and a top ferromagnetic structure
including: a thin first sublayer of material preferably of CoCr,
CoCrB or CoPtCrB, and a thicker second sublayer of material
preferably of CoPtCrB with a lower moment than the first
sublayer.
SUMMARY OF THE INVENTION
[0006] One embodiment of the invention is an antiferromagnetically
coupled (AFC) magnetic recording medium with an AFC master layer
comprising at least two magnetic layers with the top magnetic layer
including copper. The slave layer is separated from the master
layer structure by a nonmagnetic spacer layer selected to
antiferromagnetically couple the layers. The master layer structure
according to the invention includes a bottom and top layer of
distinct ferromagnetic materials. Preferably, the top layer of the
master layer is a cobalt alloy including from 1 to 5 at. % copper
with an example being CoPt.sub.13Cr.sub.20B.sub.8Cu.sub.2. In one
embodiment the middle layer is CoPt.sub.13Cr.sub.19B.sub.7, the
slave layer is CoCr.sub.10 and the spacer layer is ruthenium (Ru).
The AFC magnetic layer structure according to the invention
improves signal-to-noise ratio, increases media AC squeeze,
increases coercivity (H.sub.c), reduces side erase band and allows
higher track density while maintaining good overwrite (OW). The AFC
magnetic layer structure can be used with a variety of substrate
including glass and NiP/AlMg.
BRIEF DESCRIPTION OF THE FIGURES
[0007] FIG. 1 is a symbolic illustration of the prior art showing
the relationships between the head and associated components in a
disk drive.
[0008] FIG. 2 is an illustration of a prior art layer structure for
a magnetic thin film disk with which the antiferromagnetically
coupled magnetic layer stack of the invention can be used.
[0009] FIG. 3 is an illustration of an antiferromagnetically
coupled magnetic layer stack for a prior art magnetic thin film
disk in which the magnetic alloy according to the invention can be
used.
DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED
EMBODIMENTS
[0010] Benefits of using Cu containing magnetic alloy as the top
magnetic layer in an AFC structure: [0011] 1. Improve media
signal-to-noise ratio. [0012] 2. Increase media AC squeeze,
reducing side erase band and allowing higher track density. [0013]
3. Maintain similar OW. [0014] 4. Applicable to media on both glass
and AlMg substrates.
[0015] FIG. 2 illustrates a prior art layer structure 21 of a thin
film magnetic disk 16 in which the layer stack according to the
invention can be used. The layers under the underlayer 33 may be
any of several combinations of seed layers 32 and pre-seed layers
31 as noted in more detail below. The layer structure shown in FIG.
2 can be used with a variety of magnetic layer stacks.
[0016] The magnetic layer stack 34 is composed of a plurality of
layers which are further illustrated in FIG. 3. An embodiment of a
layer stack 34 according to the invention is an
antiferromagnetically coupled structure including a master layer
structure which has a top master magnetic layer 46 (the magnetic
layer nearest the head) and a bottom master magnetic layer 45. The
AFC spacer layer 43 separates the master layer structure from the
slave magnetic layer 44. The top layer 46 and bottom layer 45 act
together as the master layer in the antiferromagnetically coupled
structure. The top layer preferably contains from 1 to 5 at. %
copper according to the invention. A variety of cobalt alloys have
been used in the prior art for the master layer and can include
copper according to the invention. Along with copper the preferred
composition includes cobalt, platinum and chromium and the most
preferred composition is CoPtCrBCu with 10-26 at. % chromium, 11-18
at. % platinum, 4-18 at. % boron and 1-5 at. % copper.
[0017] The slave magnetic layer 44 is a ferromagnetic material of
the type used in the prior art of thin film disks. The invention
can be used with a variety of slave layer compositions. Examples of
materials suitable for slave magnetic layer 44 include CoCr,
CoCrZr, CoPtCr and CoPtCrB.
[0018] The AFC spacer layer 43 is a nonmagnetic material with a
thickness that is selected to antiferromagnetically couple the top
and middle magnetic layers 45, 46 with the slave magnetic layer 44.
Ruthenium is the preferred material for the coupling/spacer layer
43, but the prior art indicates that suitable materials include
chromium (Cr), rhodium (Rh), iridium (Ir), copper (Cu), and their
alloys. The thickness of the spacer layer 43 is according to the
prior art; for example, approximately 6 Angstroms is a preferred
target thickness for a ruthenium coupling/spacer layer 43.
[0019] Embodiments of the invention for use on circumferentially
textured NiP/AlMg and glass substrates will be described. The
bilayer AFC master layer is useful for optimizing the recording
performance of the media. The addition of copper to the AFC top
master magnetic layer is useful in this broader context. Since
NiP/AlMg substrates are electrically conductive, a bias voltage can
relatively easily be applied during the deposition of the thin
films. This allows a lower moment magnetic material to used as the
AFC bottom master magnetic layer in the bilayer master layer and a
high moment material to be used as the top layer which has certain
advantages known in the prior art. Since glass substrates are not
electrically conductive, it is more difficult to apply bias during
thin film deposition. As a result it becomes more difficult to
deposit the lower moment magnetic materials with good in-plane
c-axis characteristics as the bottom layer in the bilayer master
layer on glass substrates.
[0020] Table 1 gives the layer structure for two disks with
circumferentially textured glass substrates which are the same
except for the addition of copper to the AFC top master magnetic
layer 46 according to the invention. The layer structure is as
illustrated in FIGS. 2 and 3. The bilayer master layer in these
disks is designed to have a bottom layer with a higher moment. The
magnetic material is selected to be deposited without bias voltage
and to have good in-plane c-axis with narrow dispersion. The top
layer is selected with a lower magnetic moment with superior SNR.
TABLE-US-00001 TABLE 1 Case #1 Layer Structure On Textured Glass
Substrate CoPt.sub.13Cr.sub.17B.sub.12
CoPt.sub.13Cr.sub.20B.sub.8Cu.sub.2. CoPt.sub.13Cr.sub.19B.sub.7
CoPt.sub.13Cr.sub.19B.sub.7 Ru Ru CoCr.sub.10 CoCr.sub.10
CrTi.sub.20 CrTi.sub.20 RuAl RuAl CrTi.sub.50 CrTi.sub.50 Textured
Glass Textured Glass Substrate Substrate
[0021] Table 2 compares the recording performance of the
experimental disks according to Table 1 to isolate differences
resulting from a change resulting from adding copper to the top
magnetic layer. Each of the disks has a pre-seed layer of
CrTi.sub.50 and a seed layer of RuAl.sub.50. The RuAl has a B2
crystallographic structure. The pre-seed layer can also be CrTa or
AlTi. The pre-seed layer is amorphous or nanocrystalline. Various
crystalline underlayers such as CrTi.sub.20 or CrMo.sub.20 can be
used with the invention. The high frequency S.sub.0NR(1TS.sub.0NR)
is measured at the maximum recording density. The mid-frequency
S.sub.0NR (2TS.sub.0NR) is measured at half of the maximum
recording density. TABLE-US-00002 TABLE 2 Textured Glass Substrate
Results. Case #1 M.sub.rt H.sub.c (memu/ DCSNR 2TS.sub.0NR.sup.1
1TS.sub.0NR.sup.2 ACsqz OW (kOe) cm.sup.2) (dB) (dB) (dB) (%) (dB)
The 4.16 0.38 32.0 28.5 25.5 64.1 28.9 in- ven- tion Con- 4.02 0.38
32.0 28.3 25.2 55.3 29.1 trol Disk .sup.12TS.sub.0NR: S.sub.0NR at
half of the maximum density. .sup.21TS.sub.0NR: S.sub.0NR at the
maximum density.
[0022] In a second experiment disks were prepared with the layer
structure shown in Table 3. Each disk has an antiferromagnetically
coupled master and slave layer and a circumferentially-textured
NiP/AlMg substrate. The bilayer master layer in these disks is
designed to have a bottom layer with a lower moment. The magnetic
material is selected to be deposited with bias voltage. The top
layer is selected with a higher magnetic moment to optimize the
PW50 and resolution.
[0023] Table 4 compares the recording performance of the
experimental disks according to Table 3 to isolate differences
resulting from a change resulting from adding copper to the top
magnetic layer of the master layer according to the invention. The
slave magnetic layer in each disk is CoCr.sub.20Zr.sub.5. Although
the invention does not limit the slave layer composition, one
embodiment uses CoCrZr with 2-6 at. % Zr. Each of the disks has
multiple underlayers of Cr, CrMoB and CrMo Various crystalline
underlayers can be used with the invention. TABLE-US-00003 TABLE 3
Case #2 Layer Structure On NiP/AIMg substrate
CoPt.sub.13Cr.sub.11B.sub.15 CoPt.sub.12Cr.sub.11B.sub.15Cu.sub.2.
CoPt.sub.13Cr.sub.25B.sub.6 CoPt.sub.13Cr.sub.25B.sub.6 Ru Ru
CoCr.sub.20Zr.sub.5 CoCr.sub.20Zr.sub.5 CrMo.sub.20 CrMo.sub.20 Cr
Mo.sub.15B.sub.5 Cr Mo.sub.15B.sub.5 Cr Cr Textured NiP/AIMg
Textured NiP/AIMg Substrate Substrate
[0024] Table 4 compares the magnetic layer stack of the invention
with the control disk on a circumferentially-textured NiP/AlMg
substrate. TABLE-US-00004 TABLE 4 Textured NiP/AIMg Substrate
Results. Case #2 M.sub.rt H.sub.c (memu/ DCSNR 2TS.sub.0NR.sup.1
1TS.sub.0NR.sup.2 ACsqz OW (kOe) cm.sup.2) (dB) (dB) (dB) (%) (dB)
This 4.08 0.41 32.3 27.9 24.7 55.6 34.0 in- ven- tion Con- 4.11
0.43 32.1 27.6 24.2 50 33.9 trol Disk 1TS.sub.0NR: S.sub.0NR at the
maximum density. 2TS.sub.0NR: S.sub.0NR at half of the maximum
density.
[0025] If bias voltage can be applied during deposition of the thin
films on a non-metallic substrate such as glass, the magnetic layer
stacks described in Table 3 can be used for non-metallic substrates
as well.
[0026] The thin film structures described above can be formed using
standard thin film deposition techniques. The films can be
sequentially sputter-deposited with each film being deposited on
the previous film. The atomic percent compositions given above are
given without regard for the small amounts of contamination that
invariably exist in sputtered thin films as is well known to those
skilled in the art. The invention has been described with respect
to particular embodiments, but other uses and applications for the
ferromagnetic structure according to the invention will be apparent
to those skilled in the art.
* * * * *